The present invention relates to a pneumatic safety tire capable of running safely for a relatively long distance even in such a deflated state as a puncture, while preventing a decrease in high speed durability and steering stability.
There is an increasing demand for the so-called run-flat tires that can continue to run even if deflated by puncture or other accident. Therefore, tires provided on the inside thereof with a support member, such as a solid elastic member or an inflatable structure, to form double independent air chambers have been proposed. However, such structures significantly increase the tire weight and production cost, and therefore they are not practicable.
Meanwhile, even in ordinary non-run-flat tires or conventional pneumatic tires, if the tire is deflated, it is possible to run with the tire for a while as long as it is not displaced from the rim.
In order to prevent such dislocation from the rims, for example, in Japanese Patent Publication No. 57-15007, there are proposed a tire and rim assembly in which the tire beads are provided with radially, inwardly extending toes and the rim is provided with annular grooves to receive the bead toes to prevent the dislocation of the tire beads from the rim due to puncture.
If it is possible for conventional tires to run for a distance under a deflated condition as long as the tire is not dislocated from the rim, the sidewalls of such conventional tire must be relatively thin with the hardness thereof being low. Such a tire is inferior in its load bearing capacity, and heats up while running in such a deflated state causing the tire to break up by the heat, and hence the traveling distance is significantly limited.
Therefore, on the assumption that the rim dislocation is well controlled, it has been attempted to increase the thickness of the sidewalls for less strain, while using a relatively hard rubber with a low heat-generation property.
However, by merely increasing the thickness of hard rubber sidewall, while the run-flat performance may be slightly improved, tire performances in normal running, in particular, high speed durability, steering stability, and ride comfort, are sacrificed because of the resultant increase in the bending stiffness of the sidewall and heat generation. Thus, an increase in the sidewall thickness brings about contradictory effects on the run-flat performance and normal running performance.